The sound quality of loudspeaker transducers have been limited by unintended diaphragm material vibration modes also know as diaphragm breakup, diaphragm resonances, diaphragm ringing, modal behavior patterns, or divisional vibrations. Diaphragm material vibration modes are chaotic phenomena where diaphragm motions become highly complex and while they may develop as a consequence of the electromechanical excitation of the diaphragm 10 are generally unrelated to the aforementioned excitation. The cone vibration modes result in non-uniform velocity displacement of the diaphragm and deviation from the ideal of piston-like behavior of the diaphragm 10. The non-uniform velocity displacement causes peaks and valleys in the frequency response of the loudspeaker transducer resulting in non-linear acoustic output at varying frequencies.
The quantity, complexity, and magnitude of vibration modes exhibited by a given diaphragm 10 as part of an assembled loudspeaker transducer is highly dependent upon small variations in origin conditions that include variations in loudspeaker transducer elements including loudspeaker surrounds 11 and voice coil formers 12. Specific loudspeaker transducer diaphragm vibration modes are difficult to predict in the cone design stage and can be resistant to corrective measures that assume the diaphragm operating as one coherent mechanical element or a tightly coupled collection of coherent diaphragm regions.
Prior attempts at reducing or eliminating loudspeaker transducer diaphragm vibration modes have modeled the diaphragm either as one coherent element or as a simple assembly of several coherent sectors and attempted to correct the material vibration modes by either stiffening the diaphragm, making the diaphragm more rigid or linking or bridging coherent diaphragm regions together.
The first approach is exemplified by diaphragms with more complex cone or dome shape. This shaping may include features such as extended neck dip 21 shaping of the cone slope. A second approach is to use materials of greater inherent rigidity such as metal, fiberglass, carbon fiber, or Kevlar composite materials 20. A third approach is exemplified by diaphragms molded or stamped such that they include features like annular concentric corrugations, ribs 22 (straight, circular, or spiral), spokes, pleats, assemblies of arcuated segments, a plurality of randomly placed three-dimensional features, or diaphragms with varying thickness. Here too, the intent is to stiffen regions of the diaphragm or to stiffen the entire diaphragm.
The commonality amongst these prior art approaches is diaphragm design and manufacture without consideration of how the later attachment of a surround and a voice coil former to the diaphragm can create diaphragm material vibration modes. Loudspeaker transducers made with the aforementioned stiffening approaches can still suffer from poor acoustical quality of the radiated sound due to contamination by diaphragm material vibration modes as shown in FIGS. 6, 9, 11, and 13. While the deviations from linear response differ in detail in magnitude, center frequency, and complexity, they are alike in kind that the deviations are caused by diaphragm material vibration modes.